Fundamental Investigation of Forced Wetting on Structured Surfaces

The present work is an attempt to understand wetting on very rough surfaces for printing, coating, cooling etc. applications. Various kinds of PDMS (polydimethylsiloxane), deionized water, and glycerin-water (85%-15% vol.) mixture were used to wet the pyramidal arrays and concentric triangular circles, which have scales in millimeters. Wetting of the test substrates were done both in vertical and horizontal orientation, by dipping the substrate in a liquid bath and pumping the liquid through the center of the substrate, respectively. The apparent contact angle on each substrate was measured and a correlation between capillary number, contact angle, and feature size was sought. Existing models and contact angle evaluation methods, together with additional new approaches, have been applied and were discussed extensively. Numerical simulations for wetting on horizontally placed substrates were performed by using a C++ based, open source CFD software package, Open-FOAM (Open Source Field Operation and Manipulation). Kistler's dynamic wetting equation was implemented into the software. Simulation results compatible with experiments were achieved.